HP 41CL - Power Consumption

[Michael Fehlhammer]

Dear HP 41CL users,
I've got current supply problems with several of my CL calculators.
I have equipped them with lady cell rechargeable batteries which should have a significant higher capacity than HP's original battery pack, but a lower one than NIMH batteries, of course.
In several but not all of my CLs a calculator with fully charged batteries doesn't survive more than two weeks on the shelf, without being used. Then not even the battery indicator goes on, the calculator simply is dead. Investigation of the individual cells shows that always just one (the leftmost) is totally empty, whereas the other cells are ok. Of course we experimented with different cells.
Something must severely go wrong here. I would expect a CL with fully charged lady cells to keep its memory (without being run!) for at least two months instead of two weeks with rechargeable batteries (and several months instead of actually only 8 weeks max. with new non-rechargeable NiMH batteries). And I don't understand the onesided depletion of the set of battery cells.
Maybe electronics experts can give a hint what could be the reason of the current drain, and how to fix.
Also I'd be interested in CL owners' experience regarding battery durability (in "OFF" state, with rechargeable or with NiMH batteries).